Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Invasive Group A Streptococcus (iGAS) surveillance gets the green light: a clear-cut microbiological specimen sterility framework for comprehensive and consistent laboratory surveillance. (#40)

Andrew Fox-Lewis 1 2 3 , Juliet Elvy 2 4 5 , Sally A Roberts 2 6 , Susan C Morpeth 2 7 , Susan Taylor 2 7 , Rachel Webb 3 8 9 10
  1. Division of Infection and Immunity, Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
  2. New Zealand Microbiology Network (NZMN), New Zealand
  3. National Public Health Service Invasive Group A Streptococcus (iGAS) Clinical and Technical Advisory Group, New Zealand
  4. Microbiology Department, Awanui Labs Otago Southland, Dunedin, New Zealand
  5. The Institute of Environment Science and Research (ESR), Porirua, New Zealand
  6. Microbiology Department, LabPlus, Auckland City Hospital, Auckland, New Zealand
  7. Microbiology Department, Middlemore Hospital, Auckland, New Zealand
  8. Kidz First Children’s Hospital, Middlemore Hospital, Auckland, New Zealand
  9. Department of Paediatrics: Child and Youth Health, University of Auckland, Auckland, New Zealand
  10. Starship Children's Hospital, Auckland, New Zealand

Background

Invasive Group A Streptococcus (iGAS) infection is microbiologically defined as infection of a normally sterile body site. Existing international case definitions provide limited guidance on specimen sterility leading to inconsistent case ascertainment across public health jurisdictions. iGAS became notifiable in New Zealand (NZ) on 1 October 2024. The NZ Microbiology Network, the colleageate body representing all clinical microbiology laboratories in NZ, developed expert guidance on microbiological specimen sterility to standardise iGAS laboratory surveillance nationally.

Methods

Via consensus expert opinion, a comprehensive ‘traffic light’ specimen sterility framework was developed, stratified by specimen type (e.g. tissue) and site (e.g. brain). Specimen types were hierarchically categorised as sterile (‘green’ = blood, internal body fluids), variably sterile (‘amber’ = tissue, surgical swabs, pus) or non-sterile (‘red’ = surface swabs, excreta). Amber-type specimens include both sterile and non-sterile sites. The framework was applied to a large dataset to assess the impact of capturing cases with green-type compared to amber-type specimens. 

Results

The 3552-specimen study dataset comprised 2922 GAS infections, including 213 confirmed iGAS cases. Among iGAS cases, GAS was detected in green-type specimens in 196 (92%) and amber-type sterile site specimens in 18  (8%).

Conclusion

The proposed framework covers all common microbiological specimens and facilitates comprehensive and consistent iGAS laboratory surveillance across all jurisdictions and settings in which iGAS laboratory surveillance is conducted. Capture of iGAS cases with GAS-detection in amber-type sterile site specimens is complex. Surveillance strategies which report only GAS-detection in green-type specimens would likely still capture approximately 90% of iGAS cases.

  1. NZMN members additionally involved in development of the NZMN position statement on microbiological specimen sterility: Matthew Rogers, Irasha Harding, Matt Blakiston, Maxim Bloomfield, Anja Werno, Michael Addidle, Timothy Blackmore, Ranmini Kularatne.